1. Field of the Invention
This invention relates to noise filters and particularly to a device for substantially removing undesired correlated signal components contained in the same frequency spectrum as desired uncorrelated signal components.
2. Description of the Prior Art
Many different prior art devices, apparatuses and systems have been proposed for separating or removing noise, intersymbol interference or different signal frequencies from an input signal.
U.S. Pat. Nos. 3,857,104 (Sacks) and 3,821,482 (Hirsch) are each directed to removing unwanted noise from a noise-bearing signal. U.S. Pat. No. 3,857,104 discloses an heuristic approach to automatically weighting the audio spectrum by de-emphasizing regions where noise is "detected". This system is incapable of converging to an optimal solution and does not make use of a transversal filter. U.S. Pat. No. 3,821,482 teaches an apparatus fo noise spectrum equalization of applied power spectrum samples for enhancing the detection of signals embedded in noise. This apparatus does not utilize a transversal filter. Furthermore, the operation of this apparatus is not applicable to time-domain signals.
U.S. Pat. No. 3,911,366 (Baghdady) discloses an apparatus for separating two frequency modulated signals occupying the same channel. Since acoustic speech is an amplitude modulated process, this apparatus cannot process acoustic speech. In addition, no transversal filter is involved in the operation of this apparatus.
U.S. Pat. Nos. 3,875,515 (Stuart et al); 3,868,603 (Guidoux); 3,727,153 (McAuliffe); 3,696,203 (Leonard) and 3,609,597 (Moye) each utilize an adaptive transversal filter or automatic equalizer in an arrangement to reduce the intersymbol interference resulting from the transmission of digital data signals through a channel.
U.S. Pat. Nos. 3,809,923 (Esser); 3,660,785 (Hosokawa) and 3,614,673 (Kang) each teach the use of a transversal filter or equalizer, but do not teach speech processing. U.S. Pat. No. 3,809,923 relates to a bucket-brigade mechanization of a transversal filter. U.S. Pat. No. 3,660,785 discloses a line equalizer. U.S. Pat. No. 3,614,673 relates to an adaptive line equalizer which derives its line characteristics from a single pulse.
U.S. Pat. No. 3,845,390 (De Jager et al) teaches a system for equalizing transmission channels using an ad hoc procedure.
U.S. Pat. No. 3,715,670 (Hirsch et al) employs transversal filters to make more efficient utilization of channel bandwidth with single-sideband or vestigal-sideband transmission of synchronous digital data over a channel of limited bandwidth.
None of the above-described prior art U.S. patents teaches, shows or suggests a speech filtering device which utilizes a transversal filter to provide an estimate of only the longer correlation time-period "noise" that is contained in an input speech-bearing signal and a subtractor to subtract the longer correlation time-period "noise" from the input speech-bearing signal to obtain substantially only the shorter correlation time-period speech component of the input speech-bearing signal as the signal remmant.